1. Field of the Invention
The present invention relates to a surface preparation method for removing beforehand Si or an Si compound that exists on the surface of a substrate, or the surface of a base layer, when forming a single crystal layer of a Group III-V compound by epitaxial growth using an MOCVD (Metal Organics Chemical Vapor Deposition) method either on the surface of a substrate comprising a Group III-V compound semiconductor comprising As, or on the surface of a base layer, which is formed on the surface of this substrate, and which comprises a single crystal layer of a Group III-V compound comprising As.
Further, the present invention relates to a semiconductor is device constituted by forming either 1 or 2 or more single crystal layers of a Group III-V compound by epitaxial growth using an MOCVD method either on the surface of a substrate comprising a Group III-V compound semiconductor comprising As, or on the surface of a base layer, which is formed on the surface of this substrate, and which comprises a single crystal layer of a Group III-V compound comprising As.
2. Description of the Related Art
In a semiconductor device, such as a MESFET (Metal Semiconductor Field Effect Transistor), or a HEMT (High Electron Mobility Transistor), there are times when a Group III-V compound semiconductor, comprising a Group III element and a Group V element, is utilized as a semiconductor. For example, a GaAs semiconductor comprising Ga (Gallium) and As (Arsenic) can be utilized as this Group III-V compound semiconductor.
A semiconductor device comprising a GaAs semiconductor ordinarily has a substrate comprising a GaAs semiconductor, and either one or a plurality of single crystal layers formed on this substrate so as to sequentially overlap one another. In this case, a single crystal layer is formed in accordance with, for example, epitaxial growth, which uses the MOCVD method. Hereinafter, this single crystal layer is referred to as an epitaxial layer.
In a semiconductor device such as that mentioned above, either Si (Silicon) or an Si compound ordinarily exists in the interface between the substrate and an epitaxial layer, or in the interface of 2 adjacent re-grown epitaxial layers. When these Si or Si compounds exist, the Si acts as a donor in this interface, and carrier accumulation is generated. When this carrier accumulation is generated, leakage current and the like is generated. In accordance therewith, the characteristics of a semiconductor device deteriorate. Therefore, in a semiconductor device such as that mentioned above, It is necessary to prevent carrier accumulation resulting from Si acting as a donor.
As a method for preventing carrier accumulation resulting from Si acting as a donor, there is a surface preparation method, which prevents carrier accumulation by performing in advance prescribed processing either on the surface of a substrate, or the surface of a base layer (an epitaxial layer formed on the substrate surface) when forming an epitaxial layer. Up until now, 4 methods such as those hereinbelow could be used as this surface preparation method.
(1) A first method is one which attempts to prevent carrier accumulation resulting from Si acting as a donor by removing Si or an Si compound that exists either on the surface of the substrate, or on the surface of a base layer, in accordance with a wet etching process using either an acid or an alkali as described in Literature 1 hereinbelow.
Literature 1: J. Crystal Growth 91 (1988) 632 R. Kanber et al.
(2) A second method is a method which removes Si or an Si compound that exists either on the surface of the substrate, or on the surface of a base layer, in accordance with a gas etching process using a halogen-based gas as described in Literature 2 hereinbelow.
Literature 2: Japanese Patent Laid-open No. 5-175150
(3) A third method Is a method, which converts Si or an Si compound to a stable oxide, thereby rendering same electrically Inactive even should it be captured to the interface, by forming an oxide layer either on the surface of the substrate or on the surface of a base layer, in accordance with a UV (ultraviolet) ozone process as described In Literature 3, 4 hereinbelow.
Literature 3: Japanese Patent Laid-open No. 9-320967
Literature 4: J. Crystal Growth 133 (1993) 121 S. Izumi et al.
(4) A fourth method is a method, which oxidates and electrically passivates Si or an Si compound that has been captured to an interface, in accordance with an effect similar to that of the third method, by supplying oxygen to the surface of the substrate, or to the surface of a base layer, in accordance with an organic metal comprising a methoxy group as described in Literature 5 hereinbelow.
Literature 5: Japanese Patent Laid-open No. 10-12553
However, with the first method, although Si or an Si compound can be removed in accordance with etching, because either the surface of the substrate, or the surface of a base layer is exposed to ambient air in subsequent processes, such as rinsing, drying, and the loading into a chamber, either the surface of the substrate, or the surface of the base layer is once again contaminated by Si or an Si compound. The problem is, to avoid this contamination, the processes subsequent to etching must be processed in an environment in which Si or an Si compound do not exist, and the constitution of the semiconductor manufacturing apparatus becomes remarkably complex.
That is, in the clean rooms and clean benches used in the semiconductor industry, dust in the atmosphere is removed by filters. However, even though such a measure is taken, Si or an Si compound, which has a high intra-crustal Clarke number, readily reaches the surface of a substrate. Further, a filter is constituted of borosilicate glass. Consequently, it is extremely difficult to avoid contamination from the filter components themselves. Therefore, with this method, it is difficult to curb the interface carrier accumulation phenomenon with good repeatability.
Further, a problem with the second method is that the surface of the substrate, or the surface of a base layer becomes contaminated in accordance with the introduction of a halogen-based gas for surface processing (for gas etching). Further, a problem with this method is that the surface of the substrate, or the surface of a base layer is made rough by the gas etching process, and the surface morphology of an epitaxial layer formed on the surface of this substrate, or the surface of this base layer deteriorates. Furthermore, a problem with this method is that because a dedicated surface preparation (dedicated gas etching) gas supply line must be installed anew, the constitution of the semiconductor manufacturing apparatus becomes complex.
Furthermore, with the third method, the problem is that it is difficult to control the quantity of oxygen used to passivate Si or an Si compound, and moreover, in accordance with the oxidation of the surface of the substrate, or the surface of a base layer, the surface morphology of an epitaxial layer formed thereon deteriorates.
And furthermore, a problem with the fourth method is that, similar to the second method, the surface of the substrate, or the surface of a base layer becomes contaminated by an organic metal gas for surface preparation (for passivation). Further, a problem with this method is that, similar to the second method, because a dedicated surface preparation (dedicated passivation) gas supply line must be installed anew, the constitution of the semiconductor manufacturing apparatus becomes complex.
Accordingly, an object of the present invention is to provide a surface preparation method, which is capable of preventing carrier accumulation either in a substrate epitaxial layer interface or in an interface between regrown epitaxial layers, without making the constitution of a semiconductor manufacturing apparatus complex, without causing the contamination of either the surface of a substrate, or the surface of a base layer, and without degrading surface morphology.
Further, an object of the present Invention is to provide a semiconductor device. In which, in accordance with removing from an interface Si, which constitutes a cause of carrier accumulation, there is no carrier accumulation, and for which the constitution of a semiconductor manufacturing apparatus is not made complex, there is no contamination of either the surface of a substrate, or the surface of a base layer, and surface morphology is not degraded.
To solve for the above-mentioned problems, a surface preparation method of a first invention is a surface preparation method for removing beforehand Si or an Si compound that exists on the surface of a substrate, or on the surface of a base layer, when forming a single crystal layer of a Group III-V compound by epitaxial growth using an MOCVD method either on the surface of a substrate comprising a Group III-V compound semiconductor comprising As, or on the surface of a base layer, which is formed on the surface of this substrate, and which comprises a single crystal layer of a Group III-V compound comprising As, this surface preparation method being characterized in that it removes Si or an Si compound that exists either on the surface of a substrate, or on the surface of a base layer, in accordance with a thermal cleaning process, which utilizes an As hydride gas as the gas for cleaning.
With the surface preparation method of this first invention, Si or an Si compound that exists an the surface of a substrate, or on the surface of a base layer is removed as a hydride by a reduction reaction in accordance with free H (free hydrogen), which dissociates from the As hydride gas. In accordance therewith, Si or an Si compound can be removed, without making the constitution of a semiconductor manufacturing apparatus complex, without causing the contamination of either the surface of a substrate, or the surface of a base layer, and without degrading surface morphology. As a result thereof, it is possible to prevent carrier accumulation resulting from Si acting as a donor, without making the constitution of a semiconductor manufacturing apparatus complex.
A surface preparation method of a second invention is a method according to the first invention, wherein the supply quantity of As hydride gas is set at a supply quantity that is capable of completely removing Si or an Si compound that exists on the surface of a substrate, or on the surface of a bass layer.
With the surface preparation method of this second invention, it is possible to completely remove Si or an Si compound that exists on the surface of a substrate, or on the surface of a base layer. In accordance therewith. It is possible to completely prevent carrier accumulation resulting from Si acting as a donor.
Surface preparation methods of either a third or fourth invention according to either the first or second invention, respectively, wherein the As hydride gas is AsH3.
A semiconductor device of a fifth through an eighth invention is a semiconductor device, which is constituted by forming either 1 or 2 or more single crystal layers of a Group III-V compound by epitaxial growth using an MOCVD method, either on the surface of a substrate comprising a Group III-V compound semiconductor comprising As, or on the surface of a base layer, which is formed on the surface of this substrate, and which comprises a single crystal layer of a Group III-V compound comprising As, this semiconductor device being characterized In that the 1 or 2 or more opitaxal layers of a Group III-V compound are formed after Si or an Si compound that exists on the surface of a substrate, or on the surface of a base layer has been removed in accordance with a surface preparation method of the first through the fourth inventions.
With the semiconductor device of this fifth through eighth invention, Si or an Si compound that exists on the surface of a substrate, or on the surface of a base layer is removed in accordance with a thermal cleaning process, which uses an As hydride gas as the cleaning gas. In accordance therewith, it is possible to provide a semiconductor device in which there is no carrier accumulation, and for which the constitution of a semiconductor manufacturing apparatus is not made complex, there is no contamination of either the surface of a substrate or the surface of a base layer, and surface morphology is not degraded.